Electrically operated chucking apparatus

ABSTRACT

An electrically operated chucking apparatus including (a) an electrically operated chuck including at least two movable members movable toward and away from each other, and at least two drive devices which include respective electrically operated actuators operable to move the at least two movable members, respectively, toward and away from each other, and (b) a control device operable to control the at least two drive devices, and wherein the control device includes: a drive control portion operable to control the at least two drive devices such that each of at least one of an actual position and an actual speed of movement of the at least two movable members changes toward a predetermined target value; and a load detecting portion operable to detect a load acting on the at least two movable members during operation of the drive control portion to control the at least two drive device. The drive control portion is arranged to command the at least two drive devices to terminate movements of the at least two movable members when the load detected by the load detecting portion has increased to a predetermined threshold.

This is a Division of application Ser. No. 10/193,305 filed Jul. 12,2002, now U.S. Pat. No. 6,973,714, issued Dec. 13, 2005. The entiredisclosure of the prior application is hereby incorporated by referenceherein in its entirety.

This application is based on Japanese Patent Application No. 2001-220752filed on Jul. 19, 2001, the contents of which are incorporated hereintoby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrically operated chuckingapparatus which includes an electrically operated actuator as s drivesource and which is constructed to hold an object, such as an electricor electronic component or any other member or part.

2. Discussion of Related Art

For holding or chucking an electric or electronic component, member orpart, or any other object, there is known an electrically operated chuckdriven by an electrically operated actuator. In an electric-componentmounting system arranged to mount electric components on aprinted-wiring board or other circuit substrate, for example, such anelectrically operated chuck is used by a component-mounting headoperable to hold the electric component and transfer the electriccomponent onto the board.

The electrically operated chuck is required to hold the object with highoperating stability. To this end, the chuck is desirably arranged to beable to produce a sufficiently large chucking or holding force. Wherethe object to be held by the chuck is an electric component or any othercomparatively brittle member or part, however, the holding force shouldnot be excessively large, and should be controlled to an optimum valueto assure stable holding of the object. Further, where the object isheld by the chuck with a predetermined constant operating stroke ofchucking jaws, a variation in the dimension of a gripping portion of theobject at which the object is held will cause a variation in the holdingforce applied to the object, leading to a problem of deterioratedoperating stability of the chuck.

One considered solution to the problem indicated above is to interposean elastic body such as a rubber member or a sheet spring between thegripping portion of the chuck and the gripping portion of the object.The elastic member is expected to control the holding force owing to itselasticity or elastic deformation. To reduce the amount of variation inthe holding force of the chuck according to this solution, it isrequired to reduce the spring constant of the elastic body as much aspossible. To meet this requirement, however, the required operatingstoke of the chucking jaws of the chuck is inevitably increased,resulting in an undesirable increase in the size of the chuck, which isa problem in the field of technology in which space reduction is desiredin designing an assembly or equipment including the electricallyoperated chuck. In addition, a decrease in the spring constant of theelastic body tends to deteriorate the accuracy of positioning of theobject by the chuck when the chuck is opened to release the object.Namely, the resiliency of the elastic body may displace the object oncepositioned by the closed chuck. In this respect, the chuck using anelastic body is not suitable in the field of art requiring a high degreeof positioning accuracy of the object.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anelectrically operated chucking apparatus which is capable of holding anobject with a high degree of operating stability and which ispractically operable with reduced degrees of the problems encountered inthe prior art. This object may be achieved according to any one of thefollowing modes of the present invention in the form of an electricallyoperated chucking apparatus, each of which is numbered like the appendedclaims and depends from the other mode or modes, where appropriate, foreasier understanding of technical features disclosed in the presentapplication and possible combinations of those technical features.However, it is to be understood that the invention is not limited tothose technical features or combinations thereof, and that any one of aplurality of technical features described below with respect to any onemode of the invention may be a subject of the present invention, withoutthe other technical feature or features being combined with that onefeature.

(1) An electrically operated chucking apparatus comprising:

an electrically operated chuck comprising at least two movable membersmovable toward and away from each other, and at least two drive deviceswhich include respective electrically operated actuators operable tomove the at least two movable members, respectively, toward and awayfrom each other; and

a control device operable to control the at least two drive devices, andwherein the control device includes:

a drive control portion operable to control the at least two drivedevices such that each of at least one of an actual position and anactual speed of movement of each of the at least two movable memberschanges toward a predetermined target value; and

a load detecting portion operable to detect a load acting on the atleast two movable members during operation of the drive control portionto control the at least two drive devices,

the drive control portion commanding the at least two drive devices toterminate movements of the at least two movable members when the loaddetected by said load detecting portion has increased to a predeterminedthreshold.

In the electrically operated chucking apparatus constructed according tothe above mode (1) of this invention, the electrically operated chuckincludes the at least two movable members which are movableindependently of each other, so that the electrically operated chuck canbe more easily opened by a relatively large amount, than a conventionalchuck which uses a mechanical opening and closing device. In thisrespect, the present electrically operated chucking apparatus includingthe electrically operated chuck is advantageous for its high capabilityof holding a comparatively wide variety of objects. Since the movablemembers can be moved independently of each other, the movable memberscan hold even an asymmetric object, with a high degree of operatingstability.

The electrically operated chuck may include chucking members such aschucking jaws for holding the object. The movable members may includethe respective chucking members, such that the chucking members areformed integrally with the movable members, for example. Alternatively,the chucking members are formed separately from the movable members, andare removably attached to the respective movable members. Where thechucking members are chucking jaws, each movable member is provided withone chucking jaw formed as an integral part thereof or attached thereto,so that the chucking jaws on the at least two movable members cooperateto hold the object. For instance, the two chucking jaws are removablyattached to the respective two movable members. The chucking members maybe arranged to hold a solid or hollow object, in contact with respectiveouter surfaces of the object, or to hold a hollow object, in contactwith respective inner surfaces of the object.

The movable members are moved toward and away from each other along asingle straight line or two or more straight lines. For instance, thetwo movable members are moved relative to each other along a straightline. Alternatively, the movable members are moved in respective radialdirections toward and away from a single point on the object, forinstance, toward the center point of the object. Further alternatively,the movable members are moved toward and away from each other alongrespective circular arcs, with pivotal motions of the movable members,or with pivotal motions of support members such as arms holding therespective movable members. Linear movements of the movable membersprovide a larger distance between the adjacent movable members, and anaccordingly larger maximum opening and closing stroke, than circular orpivotal movements of the movable members. Accordingly, the electricallyoperated chuck including linearly movable members is capable of handlinga wider range of size of the objects. Where the electrically operatedchuck includes two or more movable members which are supported by a mainbody such that the movable members are linearly movable, the chuck maybe arranged such that the movable members are slidably mounted on alinear guide or guides, and are moved by respective electricallyoperated actuators while being guided by the linear guide or guides. Thedrive devices for moving the movable members use, as drive sources, theelectrically operated actuators such as DC servomotors, AC servomotors,stepping motors, and any other electric motors, which may be rotarymotors or linear motors.

Where the electrically operated chuck includes the movable members whichare linearly movable by electric motors, rotary motions of the electricmotors may be converted into linear movements of the movable members bya suitable motion-converting mechanism, which may include ballscrews andballnuts, for instance. Where the linearly movable members are moved bya linear motor or motors, the construction of the electrically operatedchuck can be simplified, in the absence of a motion-converting mechanismfor converting rotary motions into linear motions. Where the movablemembers are moved by a linear motor or motors, the electrically operatedchuck may be called “linear-motor-driven chuck”, and may include, forexample, a linearly extending stator, a pair of movable elements orarmatures movable along the stator and independently of each other, andguides arranged to guide the movable elements along the stator. In thiscase, the movable elements function as the movable members. Where thelinear motor is used, the stator of the linear motor may function as abody portion of the chuck.

The electrically operated chucking apparatus according to the above mode(1) of the present invention has the following feature or advantage.Namely, the holding force (chucking or gripping force) by which theobject is held, chucked or gripped may vary due to a variation in thedimension of the gripping portion of the object (at which the object isheld), as described previously. In view of this drawback, the loadacting on the movable members during their movements according topositioning commands or speed control commands is monitored to stop orterminate the movements of the movable members when the detected load onthe movable members has increased to the predetermined threshold value,which corresponds to an optimum holding force produced by theelectrically operated chuck to hold the object. Accordingly, the holdingforce is always optimized irrespective of the variation in the dimensionof the gripping portion of the object, permitting even an easilyelastically deformable or brittle object to be held by the chuck with ahigh degree of stability. The operation of the drive control portion ofthe control device to control the drive devices including theelectrically operated actuators will be described in greater detail,with respect to the following specific modes of the present invention.

(2) An electrically operated chucking apparatus according to the abovemode (1), wherein the drive control portion includes a drive-commandingportion operable to generate control commands from time to time, forcommanding the at least two drive devices, so as to control at least oneof the actual position and the actual speed of movement of each of theat least two movable members.

The control commands generated by the drive-commanding portion of thedrive control portion may be positioning commands to command the drivedevices to position the movable members, and/or speed control commandsto command the drive devices to control the speeds of movements of themovable members. The drive-commanding portion applies such positioningcommands and/or speed control commands to the drive devices, to move themovable members. However, the drive-commanding portion may be arrangedto apply only one positioning command or speed control command whichdefines a final position of each movable member or a desired speed ofmovement of each movable member. For a higher degree of controlaccuracy, however, the drive-commanding portion is preferably arrangedto apply positioning commands and/or speed control commands, from timeto time, such that the position or speed represented by the positioningcommands and/or speed control commands is gradually changed toward thepredetermined target value. In this case, the drive-commanding portionmay include a memory portion storing the commands to be generated atrespective points of time, and a reading portion operable to read outthe commands from time to time to be applied to the drive devices at therespective points of time. Alternatively, the drive-commanding portionmay include a command generating portion operable to generate thecommands at respective points of time, by calculation on the basis ofpredetermined equations and the time elapse, and apply the generatedcommands to the drive devices. Where the commands are applied to thedrive devices from time to time, the position and/or speed of movementof each movable member represented by the commands may be changed towardthe target value, either linearly at a constant rate, or continuously ata varying rate along a suitable curve (e.g., a sine curve).

(3) An electrically operated chucking apparatus according to the abovemode (1) or (2), wherein the load detecting portion includes a currentdetecting portion operable to detect an amount of electric currentapplied to the electrically operated actuators.

Where the movable members are moved by the electrically operatedactuators such as servomotors, the load acting on the movable members isreflected by the amount of electric current applied to the electricallyoperated actuators to drive these actuators to move the movable membersagainst the load. Namely, the holding force produced by the electricallyoperated chuck to hold the object increases with the amount of electriccurrent applied to the electrically operated actuators of the drivedevices. Therefore, the holding force by which the object is held by thechuck can be monitored by detecting the amount of electric currentapplied to the electrically operated actuators.

(4) An electrically operated chucking apparatus according to any one ofthe above modes (1)–(3), wherein the drive control portion includes amovement detecting portion operable to detect at least one of the actualposition and the actual speed of movement of each of the at least twomovable members, and drive control portion controls the at least twodrive devices on the basis of an output of the movement detectingportion.

To move and stop the movable members or change the speed of movements ofthe movable members, it is desirable to monitor the position and/orspeed of the movable members. The movement detecting portion assures animproved degree of accuracy of control of the movements of the movablemembers.

(5) An electrically operated chucking apparatus according to any one ofthe above modes (1)–(4), wherein each of the at least two movablemembers is provided with a chucking jaw having a gripping surfaceengageable with an outer surface of a gripping portion of an object tobe held by the electrically operated chuck, and the drive controlportion includes a provisional positioning control portion operable tocontrol the at least two drive devices, so as to move the at least twomovable members toward each other to respective predeterminedprovisional target positions at which an internal dimension of theelectrically operated chuck generally defined by the gripping surfacesof the chucking jaws is smaller by a predetermined amount than anexternal dimension of the gripping portion of the object.

(6) An electrically operated chucking apparatus according to any one ofthe above modes (1)–(5), wherein each of the at least two movable memberis provided with a chucking jaw engageable with an outer surface of agripping portion of an object to be held by the electrically operatedchuck, and the drive control portion includes an initial positioningportion operable to control the at least two drive devices, so as tomove the at least two movable members toward respective predeterminedinitial positions at which the chucking jaws of all of the at least twomovable members are spaced from the outer surface of the grippingportion of the object, by an equal distance, the drive control portioncontrolling the at least two drive devices to move the at least twomovable members from the predetermined initial positions toward theouter surface of the gripping portion of the object.

(7) An electrically operated chucking apparatus according to any one ofthe above modes (1)–(4), wherein each of the at least two movablemembers is provided with a chucking jaw having a gripping surfaceengageable with an inner surface of a gripping portion of an object tobe held by the electrically operated chuck, and the drive controlportion includes a provisional positioning control portion operable tocontrol the at least two drive devices, so as to move the at least twomovable members away from each other to respective predeterminedprovisional target positions at which an external dimension of theelectrically operated chuck generally defined by the gripping surfacesof the chucking jaws is larger by a predetermined amount than aninternal dimension of the gripping portion of said object.

(8) An electrically operated chucking apparatus according to any one ofthe above modes (1)–(4) and (7), wherein each of the at least twomovable member is provided with a chucking jaw engageable with an innersurface of a gripping portion of an object to be held by theelectrically operated chuck, and the drive control portion includes aninitial positioning portion operable to control the at least two drivedevices, so as to move the at least two movable members towardrespective predetermined initial positions at which the chucking jaws ofall of the at least two movable members are spaced from the innersurface of the gripping portion of the object, by an equal distance, thedrive control portion controlling the at least two drive devices to movethe at least two movable members from the predetermined initialpositions toward the inner surface of the gripping portion.

To hold the object, the chucking jaws may be moved toward each othersuch that their gripping surfaces are brought into engagement with theouter surface of the object, as in the chucking apparatus according tothe above mode (5), or may be moved away from each other such that theirgripping surfaces are brought into engagement with the inner surface ofthe object, as in the chucking apparatus according to the above mode(7). When the object is held by the chucking jaws, the chucking jaws aremoved toward the gripping portion of the object. For the chucking jawsto provide a holding force acting on the gripping portion, the chuckingjaws which are moved toward each other to hold the gripping portion atits outer surface are required to be moved to respective positions atwhich the internal dimension of the chuck generally defined by thegripping surfaces of the chucking jaws is smaller than the externaldimension of the gripping portion. On the other hand, the chucking jawswhich are moved away from each other to hold the gripping portion at itsinner surface are required to be moved to respective positions at whichthe external dimension of the chuck generally defined by the grippingsurfaces of the chucking jaws is larger than the internal dimension ofthe gripping portion. Positions of the movable members corresponding tothe above-indicated positions of the chucking jaws are referred to asthe “provisional target positions”, as described above with respect tothe above modes (5) and (7). The provisional target positions aredetermined to enable the electrically operated chuck to provide asufficiently large holding force.

In the electrically operated chucking device of the present invention,the movable members are movable by the respective drive devices,independently of each other. In other words, the movable members neednot be always moved by the same distance, and can be moved by respectivedifferent distances. In the above modes (6) and (8), the movable membersare initially moved to the respective initial positions at which all ofthe chucking jaws are spaced by the same distance from the outer orinner surface of the gripping portion of the object at which the objectis gripped by the chucking jaws. Where the movable members are movedfrom the initial positions toward the gripping portion of the object atthe same speed, the corresponding chucking jaws come into abuttingcontact with the gripping portion at the same time. Accordingly, theobject can be held by the chucking jaws, with a comparatively highdegree of positioning accuracy of the object as held by the chuckingjaws, in the electrically operated chucking apparatus constructedaccording to the above-described mode (6) or (8).

(9) An electrically operated chucking apparatus according to any one ofthe above modes (1)–(8), wherein each of the at least two movablemembers is provided with a chucking jaw engageable with a surface of agripping portion of an object to be held by the electrically operatedchuck, and the drive control portion includes a deceleration controlportion operable to reduce a speed of movement of each movable membertoward the surface of the gripping portion, after the chucking jaw hasreached a predetermined deceleration-initiating position at which thechucking jaw is spaced from the surface of the gripping portion by apredetermined distance.

For reducing a shock or impact upon abutting contact of the chuckingjaws with the gripping portion of the object, it is desirable tominimize the speed of movement of each movable member toward thegripping portion. In this respect, the chucking apparatus according tothe above mode (9) arranged to reduce the speed of movement of eachmovable member at a position shortly before the surface of the grippingportion is less likely to suffer from damaging of the object, andassures improved positioning accuracy of the object as held by thechucking jaws. The deceleration control portion may be adapted to reducethe movement speed of each movable member in steps, or continuouslyalong a straight line or a curve (e.g., a sine curve).

(10) An electrically operated chucking apparatus according to any one ofthe above modes (1)–(9), wherein the drive control portion includes afinal-target-position holding control portion operable to determine, asfinal target positions of the at least two movable members, actualpositions of the at least two movable members upon detection by the loaddetecting portion that the load has increased to the predeterminedthreshold, the final-target-position holding control portion controllingsaid at least two drive devices to hold the at least two movable membersat the final target positions.

(11) An electrically operated chucking apparatus according to the abovemode (10), wherein the drive control portion further includes aload-detection inhibiting portion operable to inhibit the detection ofthe load while the at least two movable members are held at the finaltarget positions under the control of the final-target-position holdingcontrol portion.

The object can be held by the chuck with a desired holding force whenthe movements of the movable members are terminated when the detectedload acting on the movable members has increased to the predeterminedthreshold. However, the object held by the chuck may be displacedrelative to the chuck due to some external force exerted onto theobject, for instance, due to movements of the movable member an inertialforce which may be generated when the chuck is moved with the object. Inthe electrically operated chucking apparatus according to the above mode(10), the movable members are held at the final target positions whichare the actual positions of the movable members when the detected loadon the movable members has increased to the predetermined threshold.Accordingly, the object can be held by the chuck with a comparativelyhigh degree of stability in the positioning accuracy of the object.While the movable members are held at the final target positions, it isnot necessary to continue the detection of the load by the load on themovable member. In this respect, the detection of the load by the loaddetecting portion may be inhibited by the load-detection inhibitingportion, as in the above mode (11).

(12) An electrically operated chucking apparatus comprising:

an electrically operated chuck comprising at least two movable membersmovable toward and away from each other, and at least two drive deviceswhich include respective electrically operated actuators operable tomove the at least two movable members, respectively, toward and awayfrom each other; and

a control device operable to control the at least two drive devices,

and wherein the control device includes a drive control portion operableto control the at least two drive devices such that each of at least oneof an actual position and an actual speed of movement of each of the atleast two movable members changes toward a predetermined target value,and such that an amount of electric current applied to each of theelectrically operated actuators does not exceed a predetermined upperlimit.

The electrically operated chuck of the chucking apparatus according tothe above mode (12) is controlled in a manner different from that of theelectrically operated chuck of the chucking apparatus according to anyone of the above modes (1)–(11), which includes load detecting portionoperable to detect the load acting on the movable members and a drivecontrol operation arranged to determine whether the detected load hasreached a predetermined threshold corresponding to the optimum holdingforce by which the object is held by the electrically operated chuck.The chucking apparatus according to the above mode (12) does not includesuch a load detecting portion, but includes a drive control portionarranged to monitor an amount of electric current applied to eachelectrically operated actuator to move the corresponding movable member.The drive control portion monitors the amount of electric current ofeach electrically operated actuator, as a parameter representative ofthe load acting on each movable member. This drive control portion isfurther arranged to control the drive device such that the amount ofelectric current does not exceed a predetermined upper limitcorresponding to the optimum holding force. Accordingly, theelectrically operated chuck does not produce an excessively largeholding force, which would be produced if the amount of electric currentof the electrically operated actuator exceeded the predetermined upperlimit. Thus, the holding force is always optimized irrespective of avariation in the dimension of the gripping portion of the object,permitting even an easily elastically deformable or brittle object to beheld by the chuck with a high degree of stability. The drive controlportion of the control device of the present chucking apparatus may beconsidered to have a current limiting function of limiting the amount ofelectric current applied to the electrically operated actuators.Alternatively, the control device may be considered to include a currentlimiting portion operable to perform such a current limiting function,as well as the drive control portion. The operation of the drive controlportion of the control device will be described in greater detail, withrespect to the following specific modes of the present invention. It isto be understood that the foregoing descriptions on the movable members,electrically operated actuators, etc. with respect to the above mode (1)apply to the electrically operated chucking device according to theabove mode (12).

(13) An electrically operated chucking apparatus according to the abovemode (12), wherein the drive control portion includes a drive-commandingportion operable to generate control commands from time to time, forcommanding the at least two drive devices, so as to control at least oneof the actual position and the actual speed of movement of each of theat least two movable members.

The drive-commanding portion in the chucking apparatus according to theabove mode (13) has the same significance as the drive-commandingportion in the chucking apparatus according to the above mode (2). It isto be understood that the features described above with respect to theabove modes (4)–(9) are equally applicable to the chucking apparatusaccording to the above mode (12) or (13).

(14) An electrically operated chucking apparatus according to the abovemode (13), wherein the drive control portion includes afinal-target-position holding control portion operable to determine, asfinal target positions of the at least two movable members, actualpositions of the at least two movable members after the amount ofelectric current applied to each of the electrically operated actuatorshas been limited to the predetermined upper limit and after a moment ofdetermination by the drive control portion that all of the controlcommands supplied from the drive-commanding portion have been executed,the final-target-position holding control portion controlling the atleast two drive devices to hold the at least two movable members at thefinal target positions.

Where the drive devices are provided with the control commands that aresuccessively supplied from the drive-commanding portion, even after themovable members come into abutting contact with the gripping portion ofthe object, the optimum holding force is established after execution ofall control commands, since the amount of electric current applied tothe electrically operated actuators of the drive devices is limited tothe predetermined upper limit which corresponds to the optimum holdingforce. In the chucking apparatus according to the above mode (14)wherein the movable members are held at the final target positions whichare the positions after all of the control commands have executed, theobject is not displaced relative to the electrically operated chuck dueto any external force exerted onto the object. Thus, the chuckingapparatus according to the above mode (14) permits improved stability inthe positioning accuracy of the object as held by the electricallyoperated chuck.

(15) An electrically operated chucking apparatus according to the abovemode (14), wherein the final-target-position holding control portiondetermines, as the final target positions, the actual positions of theat least two movable members when a predetermined time has passed afterthe amount of electric current applied to each electrically operatedactuator has been limited to the predetermined upper limit and after allof the control commands have been executed.

The predetermined time used in the chucking apparatus according to theabove mode (15) is determined such that the state in which the object isheld by the chuck is stabilized. Accordingly, the movable members areheld at the final target positions that are the positions after theholding state of the object is stabilized, that is, after the holdingforce is stabilized at the optimum value corresponding to the upperlimit of the electric current applied to the electrically operatedactuators. Thus, the electrically operated chuck of the present chuckingdevice assures a high degree of stability in the holding force.

(16) An electrically operated chucking apparatus according to the abovemode (14) or (15), wherein the drive control portion further includes acurrent limitation canceling portion operable to inhibit limitation ofthe amount of electric current to the predetermined upper limit whilethe at least two movable members are held at the final target positionsby the final-target-position holding control portion.

The object may be displaced relative to the chuck due to an externalforce, for example, after the holding of the movable members at thefinal target positions is initiated. To permit the displaced object tobe restored to the final target positions, it is preferable not to limitthe drive forces of the electrically operated actuators to move themovable members, that is, not to limit the amounts of electric currentapplied to the actuators. In the chucking apparatus according to theabove mode (16) in which the current limitation to the upper limit iscancelled while the movable members are held at the final targetpositions, the object can be held by the chuck with a relatively highdegree of stability in the positioning accuracy of the object. Where thedrive control portion of the control device of the present chuckingapparatus has a current limiting function of limiting the amount ofelectric current applied to the electrically operated actuators, asdescribed above, the current limitation canceling portion inhibits anoperation of the drive control portion to perform the current limitingfunction. Where the control device includes a current limiting portionoperable to perform such a current limiting function as well as thedrive control portion, the current limitation canceling portion inhibitsan operation of the current limiting portion.

(17) An electrically operated chucking apparatus according to any one ofthe above modes (10) and (14)–(16), wherein the electrically operatedchuck is movable to receive an object to be held thereby, from anobject-supporting member, and the final-target-position holding controlportion determine, as the final target positions, the actual positionsof the at least two movable members after the object held by theelectrically operated chuck is separated from the object-supportingmember.

The electrically operated chuck of the chucking apparatus according tothe above mode (17) is arranged to receive and hold the object assupported by the object-supporting member, for instance, to receive theobject supported on an object support table, and is then moved with theobject away from the object-supporting member. In this chuckingapparatus, the object is held by the chuck while the object is supportedby the object-supporting member. Therefore, the state in which theobject is held by the chuck may be influenced by the object-supportingmember. For instance, the object as held by the chuck may be more orless inclined from the nominal position relative to the chuck, due to aforce of friction between the object and the object-supporting member.In this case, the influence of the object-supporting member iseliminated immediately after the object is moved with the chuck apartfrom the object-supporting member, so that the state in which the objectis held by the chuck may vary after the object is separated from theobject-supporting member, that is, may be brought into its nominalposition relative to the chuck. In view of this possibility, the holdingof the movable members at the final target positions is desirablyinitiated after the influence of the object-supporting member on theobject is eliminated, that is, after the movable members are separatedfrom the object-supporting member. In this respect, the chuckingapparatus according to the above mode (17) is advantageous for itsrelatively high degree of stability in the positioning accuracy of theobject as held by the chuck after the object is separated from theobject-supporting member.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, advantages and technical andindustrial significance of the present invention will be betterunderstood by reading the following detailed description of preferredembodiments of the invention, when considered in connection with theaccompanying drawings, in which:

FIG. 1 is a schematic plan view of an electric-component mounting systemusing an electrically operated chucking apparatus including aliner-motor-driven chuck, which chucking apparatus is constructedaccording to one embodiment of this invention;

FIG. 2 is a side elevational view showing a vicinity of thelinear-motor-driven chuck in the electric-component mounting system ofFIG. 1;

FIG. 3 is a front elevational view showing the vicinity of thelinear-motor-driven chuck;

FIG. 4 is a plan view of the linear-motor-driven chuck;

FIG. 5 is a front elevational view of the linear-motor-driven chuck;

FIG. 6 is a side elevational view in cross section of thelinear-motor-driven chuck;

FIGS. 7A and 7B are views for explaining installation and removal ofchucking jaws of the linear-motor-driven chuck;

FIG. 8 is a block diagram showing a portion of a control device of theelectric-component mounting system, which portion relates to the presentinvention;

FIG. 9 is a flow chart illustrating a printed-wiring board assemblingroutine executed by the control device according to a control program;

FIG. 10 is a flow chart illustrating a component chucking routineexecuted in step S3 of the routine of FIG. 9;

FIG. 11 is a flow chart illustrating a component mounting routineexecuted in step S7 of the routine of FIG. 9;

FIG. 12 is a flow chart illustrating a component chucking routineexecuted in place of the routine of FIG. 10, in another embodiment ofthis invention;

FIG. 13 is a flow chart illustrating a component chucking routineexecuted in a further embodiment of this invention;

FIG. 14 is a flow chart illustrating a component chucking routineexecuted in a still further embodiment of this invention;

FIG. 15 is a flow chart illustrating a component chucking routineexecuted in still another embodiment of this invention;

FIGS. 16A and 16B are views schematically showing a problem which maytake place if the linear-motor-driven chuck is elevated while thechucking jaws of the chuck are maintained at final target positionsdetermined before the elevation of the chuck; and

FIG. 17 is a bottom plan view of a linear-motor-driven chuck used in anelectrically operated chucking device according to a further embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will be described in detail several embodiments of theelectrically operated chucking apparatus of the present invention, whichare adapted to be used in an electric-component mounting system, to holdan object in the form of an electric component to be mounted on aprinted-wiring board.

Referring first to the plan view of FIG. 1, the electric-componentmounting system has a machine base 10 on which are mounted a substrateconveyor 12, a component-supplying device 16 and a component-mountingdevice 18. The substrate conveyor 12 is arranged to feed a circuitsubstrate in the form of the printed-wiring board indicated at 14. Thesubstrate conveyor 12 is further arranged to support and position theprinted-wiring board 14 at a predetermined component-mounting position.Thus, the substrate conveyor 14 also functions as a substrate supportingdevice. The component-supplying device 16 includes two component supplytables 20, and a plurality of object-supporting members in the form ofcomponent feeders 19 which are mounted on the component supply tables 20and each of which accommodates a multiplicity of electric componentssuch that the electric components of different kinds are supplied fromthe respective component feeders 19. On each of the two component supplytables 20, the component feeders 19 are mounted such that componentsupply portions of the component feeders 19 are arranged along astraight line parallel to an X-axis direction. Each component supplytable 20 is movable on a pair of guides 22, in a Y-axis directionbetween an operating position or component-supply position of FIG. 1 anda non-operating position or retracted position.

The component-mounting device 18 has an XY positioning device, whichincludes a Y-axis slide 34 movable in the Y-axis direction perpendicularto the X-axis direction, and an X-axis slide 40 movable in the X-axisdirection. The Y-axis slide 34 is slidably mounted on a pair of guides28 which are supported by supported posts 26 fixedly provided on themachine base 10 and which extend in the Y-axis direction. The Y-axisslide 34 is moved in the Y-axis direction by a Y-axis drive motor(servomotor) 32 through a pair of feedscrews 30 extending parallel tothe guides 28. The X-axis slide 40 is mounted on the Y-axis slide 34such that the X-axis slide 40 is movable in the X-axis direction by anX-axis drive motor (servomotor) 38 through a feedscew 36. The X-axisslide 40 carries a component-mounting head 44, which is arranged toreceive each electric component supplied from the component-supplyingdevice 16. The X-axis slide 40 and the Y-axis slide 34 are moved to movethe component-mounting head 44, for mounting the electric component at apredetermined component-mounting spot on the printed-wiring board 14. Animage-taking device 48 incorporating a line sensor 46 is fixedlydisposed on the machine base 10, to take an image of the electriccomponent as held by the component-mounting head 44, during a movementof the head 44 from the component-receiving position to a position rightabove the component-mounting spot corresponding to the electriccomponent.

As shown in FIGS. 2 and 3, the component-mounting head 44 includes amain body in the form of a vertically movable member 50 which is movableon the X-axis slide 40 in a vertical or Z-axis direction perpendicularto the XY plane. This vertically movable member 50 is slidably mountedon a pair of guides 52 provided on the X-axis slide 40, and is moved bya Z-axis drive motor (servomotor) 56 through a feedscrew 54. A rotarymotion of the Z-axis drive motor 56 (shown in FIG. 8) is transmitted tothe feedscrew 54 through a transmission including a timing pulley 58. Arotary shaft 62 is mounted on the vertically movable member 50 through apair of bearings 60 such that the rotary shaft 62 extends in the Z-axisdirection and is rotatable but axially immovable relative to thevertically movable member 50. The rotary shaft 50 is rotated by a θ-axisdrive motor (servomotor) 64 through a pinion 66 and a gear 68.

A body portion of the gear 68 is formed integrally with the lower endportion of the rotary shaft 62. To the body portion of the gear 68,there is removably attached a linear-motor-driven chuck 72 (hereinafterreferred to simply as “chuck 72”) of the electrically operated chuckingapparatus constructed according to the present embodiment. Describedmore specifically, a mounting member 76 is fixed to the lower end faceof the body portion of the gear 68 through a pair of connecting rods 74.The chuck 72 includes an electrically operated actuator in the form of alinear motor 80 having a stator 82, and is removably attached at thestator 82 to the mounting member 76. The linear motor 80 is a linear DCbrushless motor, which includes the above-indicated stator 82, a pair ofarmatures in the form of a pair of movable elements 84, 86, and a pairof guides 88 for guiding the movable elements 84, 86 in the longitudinaldirection of the stator 82. The chuck 72 is shown in the plan view ofFIG. 4 and the front elevational view of FIG. 5.

The stator 82 has a main body 90 formed of a non-magnetic material, moreprecisely, an aluminum alloy, and a multiplicity of permanent magnets 92fixedly embedded in the main body 90. Each permanent magnet 92 is aprismatic member having a rectangular cross sectional shape and twoopposite surfaces parallel to the front and rear surfaces of the mainbody 90. The two opposite surfaces of each permanent magnet 92 arepolarized as N and S poles, respectively. The permanent magnets 92 arepositioned on the main body 90 such that the N-pole surface and theS-pole surface of each permanent magnet 92 are spaced from the front andrear surfaces of the main body 92 by a small distance in the directionof thickness of the main body 92, and such that the permanent magnets 92are spaced apart from each other in the longitudinal direction of thestator 82 while the N-pole and S-pole surfaces are arranged alternatelyin the longitudinal direction of the stator 82 on each of the front andrear surfaces of the main body 90.

Each of the two movable elements 84, 86 is provided with two iron cores96 which are opposed to the respective opposite front and rear surfacesof the stator 82 and which are connected at their lower ends to eachother by a table 98, such that the two iron cores 96 and the table 98cooperate to constitute a generally U-shaped structure. Each iron core96 is provided with a U-phase coil winding, a V-phase coil winding and aW-phase coil winding, which cooperate to form a coil unit. Bycontrolling an armature current to be applied to the coil units of thetwo iron cores 96, a linearly moving force produced by an interactionbetween magnetic forces generated by the coil windings and magneticforces of the permanent magnets 92 of the stator 82 is controlled whenthe movable element 84, 86 is linearly moved by the linearly movingforce along the stator 82.

The movements of the movable elements 84, 86 are guided by the twoguides 88 fixed to the respective front and rear surfaces of the stator82. The generally U-shaped structure of each movable element 84, 86 hastwo sliders 100 fixed to respective inner surfaces thereof opposed tothe front and rear surfaces of the stator 82. These sliders 100 are heldin engagement with the respective guides 88 via balls, so that themovable elements 84, 86 are slidably movable on the guides 88. In thepresent embodiment, the electrically operated actuator in the form ofthe linear motor 80 constitutes a main body portion of the electricallyoperated chuck in the form of the linear-motor-driven chuck 72, and thetwo movable elements 84, 86 function as a pair of movable members. Thelinear motor 80 operable to move the movable elements 84, 86 may beconsidered to function as a pair of electrically operated actuators formoving the pair of movable members. The linear motor 80 may also beconsidered to function as a drive device for driving the movablemembers, and the stator 82 may be considered to constitute a main bodyof the chuck 72, which functions to hold the movable members and theelectrically operated actuator.

The two movable elements 84, 86 have respective zero points at thelongitudinal opposite ends of the stator 82. These zero points aredetected by respective zero-point detectors 102, 103 (shown in FIG. 8),and the positions of the movable elements 84, 86 are detected byrespective position detectors 104, 106 (also shown in FIG. 8). Thepositions of the movable elements 84, 86 are represented by theirdistances from their zero points. In the present embodiment, each of thezero-point detectors 102, 103 is a photoelectric sensor of lightemitting type including a light emitting element (LED) serving as alight emitter, and a photo-detector whose output changes depending uponwhether a light emitted by the light emitter is received or not. Eachmovable element 84, 86 carries a shutter member, and the light emitterand the photo-detector are positioned such that the shutter isinterposed between the light emitter and the photo-detector when themovable element 84, 86 has reached its zero point. However, thezero-point detectors 102, 103 may be any other type of sensor ordetector such as a photoelectric sensor of light reflecting type, alimit switch or other contact-type detector, and a proximity switch. Onthe other hand, each of the position detectors 104, 106 is a magnetictype linear scale (so-called “magne-scale”) including a magneticdetector head carried by each movable element 84, 86, and a magneticscale which is magnetically calibrated and read by the magnetic detectorhead. A distance of displacement of each movable element 84, 86 isdetected on the basis of an electric signal generated by the magneticdetector head. However, the position detectors 104, 106 may be any othertype of sensor or detector, such as an optical type linear scale. Asingle magnetic scale may be used commonly for the two positiondetectors 104, 106.

Two chucking jaws 108, 109 which cooperate to function as chuckingmembers for holding the electric component are removably attached to therespective tables 98 of the two movable elements 84, 86. A plurality ofsets of chucking jaws 108, 109 of different configurations (differentsizes and shapes) are prepared for respective different kinds ofelectric components to be held by the chuck 72. Namely, the chuckingjaws 108, 109 are changed depending upon the specific kind of theelectric component to be chucked. The table 98 of each movable element84, 86 has a jaw holder 110 and a positioning pin 111 fixed thereto,while each chucking jaw 108, 109 has a tapered shank 112, as shown inenlargement in FIG. 7A. The tapered shank 112 has an annular engaginggroove 113 formed in its outer circumferential surface. The jaw holder110 has a tapered hole formed therein, and a U-shaped retainer 114 fixedthereto. The U-shaped retainer 114 is an elastic member having a pair ofopposed parallel arms. When the tapered shank 112 is fitted into thetapered hole in the jaw holder 110, the pair of arms of the U-shapedretainer 114 are elastically brought into engagement with the annularengaging groove 113, to thereby prevent the chucking jaw 108, 109 frombeing removed from the jaw holder 110. Further, the free end portion ofthe positioning pin 111 is inserted into a positioning hole formed ineach chucking jaw 108, 109, so that the chucking jaw 108, 109 ispositioned in its circumferential direction of the tapered shank 112relative to the jaw holder 110 and is prevented from being rotated.While the chucking jaws 108, 109 serving as the gripper are removablyattached to the movable elements 84, 86 serving as the movable members,the gripper may be formed integrally with each movable element 84, 86.The chucking jaws 108, 109 shown in FIG. 7A are formed to hold theelectric component, in contact with the outer surface of the electriccomponent, while the chucking jaws 108, 109 shown in FIG. 7B are formedto hold the electric component, in contact with the inner surface of theelectric component.

Each chucking jaw 108, 109 has a gripper portion provided with anelastic member in the form of a rubber plate 107, which has a grippingsurface engageable with the outer surface of a gripping portion of theelectric component at which the electric component is held by thechucking jaws 108, 109. The rubber plate 107 functions as a shockabsorber or damper when the gripper portion is brought into abuttingcontact with the electric component, i.e., an object to be chucked. Therubber plate 107 also functions as a friction member for giving asuitable amount of friction force between the gripper portion and theobject. As described below in detail, the object holding force to beproduced by the present electrically operated chuck 72(linear-motor-driven chuck) can be electrically controlled, so that thespring constant of the rubber lining 107 need not be made as low asrequired in the prior art, that is, may be made comparatively high byusing a comparatively hard rubber material and forming the rubber lining107 with a comparatively small thickness. In the electric-componentmounting system described above wherein the component-mounting head 44holding the electric component is moved in the X-axis and Y-axisdirections, the movable elements 84, 86 may be subject to an inertialforce, which may reduce the holding force for holding the electriccomponent. However, the resiliency of the rubber linings 107 effectivelyprevents an excessive amount of reduction of the holding force due tothe inertial force. In this respect, the rubber linings 107 alsofunction as a member to prevent reduction of the holding force.

The set of chucking jaws 108, 109 is automatically changed dependingupon the specific kind of the electric component to be held by the chuck72. To this end, the sets of chucking jaws 108, 109 are accommodated ina jaw accommodating device 115 disposed between the component-supplyingdevice 16 and the substrate conveyor 12, as shown in FIG. 1. When theset of chucking jaws 108, 109 presently mounted on the movable elements84, 86 is replaced by another set of chucking jaws 108, 109, the chuck72 is moved to a position right above the jaw accommodating device 115,and is lowered until the jaws 108, 109 are brought into engagement witha jaw detaching member which is provided within the jaw accommodatingdevice 115 and which is operable to remove the jaws 108, 109 from thechuck 72 when the chuck 72 is elevated away from the jaw accommodatingdevice 115. The removed jaws 108, 109 is accommodated within the jawaccommodating device 115. The new set of chucking jaws 108, 109 isattached to the movable elements 84, 86 by a downward of the chuck 72.Since the understanding of the manner of changing the chucking jaws 108,109 is not essential to understand the principle of this invention, nodetailed description in this respect is deemed necessary. Brieflydescribed, the chucking jaws 108, 109 can be easily attached and removedto and from the jaw holders 110 of the chuck 72 by applying a suitableamount of force to the tapered shanks 112 in the axial direction.

The electric-component mounting is controlled by a control device 116.FIG. 8 shows only those elements of the control device 116 which relateto the present invention. The control device 116 is constitutedprincipally by a computer 118 which incorporates a processing unit (PU)120, a read-only memory (ROM) 122, a random-access memory (RAM) 124, aninput port 126, and an output port 127, which are interconnected to eachother by a bus line. To the input port 126, there are connected an imagedata processing computer 130 operable to process image data obtained bythe image taking device 48, the zero-point detectors 102, 103, theposition detectors 104, 106, and two current detectors 128, 129 providedto detect amounts of electric currents applied to the movable elements84, 86 of the linear motor 80. The current detectors 128, 129 alsofunction as load detectors for detecting loads acting on the movableelements 84, 86. To the output port 127, there are connected throughdriver circuits the Y-axis drive motor 32, the X-axis drive motor 38,the Z-axis drive motor 56, the θ-axis drive motor 64 and the movableelements 84, 86. The ROM 122 stores various control programs such as aprogram for executing a printed-wiring-board assembling routineillustrated in the flow charts of FIGS. 9–11, for controlling theelectric-component mounting system to automatically mounts the electriccomponents on the printed-wiring board 14, so as to fabricate aprinted-circuit board. The printed-wiring-board assembling routine willbe described, assuming that the chucking jaws 108, 109 of the type shownin FIG. 7A are used.

When the printed-wiring board 14 has been positioned at thecomponent-mounting position by the substrate conveyor 12, the routine ofFIG. 9 is initiated with step S1 to read out component data relating tothe electric component to be mounted next on the board 14. The componentdata include component-kind data indicative of the kind of the nextelectric component, receiving-position data indicative of thepredetermined component-receiving position at which the next electriccomponent is received by the chuck 72, and mounting-spot data indicativeof the predetermined component-mounting spot on the board 14 at whichthe next electric component is to be mounted. Step S1 is followed bystep S2 in which the chuck 72 is moved, according to the component data,to the component-receiving position at which the chuck 72 receives theelectric component. Then, the control flow goes to step S3 in which acomponent chucking routine is initiated.

The component chucking routine, which is illustrated in the flow chartof FIG. 10, is initiated with step S11 in which the chucking jaws 108,109 are moved to predetermined initial positions at which the chuck 72is in an open state. Described in detail, the initial positions of thechucking jaws 108, 109 are determined such that the surfaces of the tworubber linings 107 of the jaws 108, 109 located at the initial positionsare theoretically spaced from a predetermined same distance from therespective outer surfaces of the electric component with which therubber linings 107 come into abutting contact, to hold the electriccomponent located at the component-receiving position. The initialposition of each chucking jaw 108, 109 is determined for each of thedifferent kinds of the electric components, and is represented by aninitial-position distance from a reference position of the grippingportion of the electric component at which the electric component is tobe held by the chucking jaws 108, 109. Distance data sets indicative ofthe different initial-position distances for the different kinds of theelectric components are stored in the RAM 124, and one of the distancedata sets which corresponds to the specific kind of the electriccomponent to be chucked is read out from the RAM 124, according to thecomponent-kind data, for each of the chucking jaws 108, 109 (for each ofthe movable elements 84, 86). The moving elements 84, 86 are movedaccording to the read-out distance data set, so that the chucking jaws108, 109 are moved to the initial positions. It will be understood thata portion of the control device 116 assigned to implement step S11constitutes an initial positioning portion operable to move the chuckingjaws 108, 109 to the predetermined initial positions. It is noted thatthe chucking jaws 108, 109 are moved to the initial positions in theX-axis direction. That is, the movements of the chucking jaws 108, 109to the initial positions are effected while the chuck 72 is positionedin the rotating direction of the rotary shaft 62, so as to be placed inan angular position at which the chucking jaws 108, 109 are moved in theX-axis direction.

The above-indicated reference position of the gripping portion of theelectric component is aligned with the centerline of the chuck 72, thatis, the axis of rotation of the rotary shaft 62 when the chuck 72 isattached to the mounting member 76. Accordingly, the chucking jaws 108,109 are moved by the same distance to their initial positions,symmetrically with respect to a plane including the axis of rotation ofthe rotary shaft 62, where the electric component is symmetric withrespect to a plane perpendicular to the direction of movements of thetwo chucking jaws 108, 109 toward and away from each other. Where theelectric component is asymmetric with respect to the above plane, thechucking maws 108, 109 are moved by different distances to their initialpositions, asymmetrically with respect to the plane including the axisof rotation of the rotary shaft 62. It will be understood that theportion of the control device 116 assigned to implement step S11 of thecomponent chucking routine of FIG. 10 constitutes an object-adaptivecontrol portion operable to control the chuck 72 such that the chuck 72is opened to its initial position, in a manner adapted to the kind orconfiguration of the electric component. Namely, the object-adaptivecontrol portion is considered to include a symmetric control portionoperable to open the chuck 72 to its initial position, with symmetricmovements of the chucking jaws 108, 109 when the electric component hasa symmetric configuration, and an asymmetric control portion operable toopen the chuck to its initial position, with asymmetric movements of thechucking jaws 108, 109 when the electric component has an asymmetricconfiguration.

After the chucking jaws 108, 109 have been moved to their initialpositions the control flow goes to step S12 in which the verticallymovable member 50 is lowered by the Z-axis drive motor 56 to lower thechuck 72 to a level at which the chuck 72 holds the electric componentindicated at 134 in FIG. 3. Then, the control flow goes to step S13 inwhich the movable elements 84, 86 are driven according to positioningcommands to move the chucking jaws 108, 109 to hold the electriccomponent 134. At this time, the positions of the chucking jaws 108, 109are continuously detected by the position detectors 104, 106, while theamounts of electric current I applied to the movable elements 84, 86 ofthe linear motor 80 are continuously detected by the current detectors128, 129. It will be understood that the position detectors 104, 106 anda portion of the control device 116 assigned to detect the positions ofthe chucking jaws 108, 109 on the basis of the output signals of theposition detectors 104, 106 cooperate to constitute a movement detectingportion operable to detect the positions of the chucking jaws 108, 109.It will also be understood that the current detectors 104, 106 and aportion of the control device 116 assigned to detect the amount ofelectric current I on the basis of the output signals of the currentdetectors 104, 106 cooperate to constitute a current detecting portionoperable to detect the amounts of electric current I applied to themovable elements 84, 86, and a load detecting portion operable to detecta load acting on the chucking jaws 108, 109.

In step S13, the movable elements 84, 86 are controlled to move thechucking jaws 108, 109 from the initial positions toward the outersurfaces of the electric component to be held by the chuck 72. Describedin detail, the chucking jaws 108, 109 are moved to predeterminedprovisional target positions at which a distance between the chuckingjaws 108, 109 is smaller by a predetermined small amount than anexternal dimension of the gripping portion of the electric component.This predetermined small amount is determined so as to absorb oraccommodate an expected maximum amount of variation of the externaldimension of the gripping portion of the electric component. The movableelements 84, 86 are commanded to be moved to the predeterminedprovisional target positions according to positioning commands generatedby suitable drivers. It will be understood that a portion of the controldevice 116 assigned to implement step S13 constitutes a drive-commandingportion operable to command the movable elements 84, 86 to move thechucking jaws 108, 109 to the provisional target positions, and aprovisional positioning control portion operable to effect provisionalpositioning of the chucking jaws 108, 109.

Step S13 is followed by step S14 to determine whether a DECELERATIONflag F1 (which will be described) is set at “1”. When step S13 isimplemented for the first time, that is, immediately after the movementsof the chucking jaws 108, 109 toward the provisional target positions isinitiated, a negative decision (NO) is obtained in step S14, and thecontrol flow goes to step S15 to determine whether the chucking jaws108, 109 have reached a predetermined deceleration-initiating positionat which the speed of the movements of the chucking jaws 108, 109 isreduced. The deceleration-initiating position is spaced apart from theouter surfaces of the gripping portion of the electric component by apredetermined distance in directions toward the initial positions. Thedeceleration-initiating position is changed depending upon the specifickind of the electric component, and deceleration-initiating data setsindicative of the different deceleration-initiating positions for thedifferent kinds of electric components are stored in the RAM 124. Thedeceleration-initiating position for each kind of electric component isdetermined while taking into account the expected maximum amount ofvariation in the external dimension of the gripping portion of theelectric component. When an affirmative decision (YES) is obtained instep S15, the control flow goes to step S16 to decelerate the chuckingjaws 108, 109, so that the chucking jaws 108, 109 are brought intoabutting contact with the gripping portion, with a reduced amount ofshock or impact. In the present embodiment, the chucking jaws 108, 109are moved at a relatively high speed until the affirmative decision isobtained in step S15, and at a relatively low speed after theaffirmative decision is obtained in step S15. Namely, the speed ofmovements of the chucking jaws 108, 109 is reduced in step S16. Themovements at the relatively high speed are achieved by generation ofpositioning commands at a relatively high frequency, while the movementsat the relatively low speed are achieved by generation of thepositioning commands at a relatively low frequency. In step S16, theabove-indicated DECELERATION flag F1 is set to “1”, so that when stepS14 is implemented in the subsequent control cycles, an affirmativedecision (YES) is obtained in step S14, and the control flow goes tostep S17, while skipping steps S15 and S16. It will be understood that aportion of the control device 116 assigned to implement steps S15 andS16 constitutes a deceleration control portion operable to deceleratethe chucking jaws 108, 109 when the jaws have reached the predetermineddeceleration-initiating position.

Further movements of the chucking jaws 108, 109 after their abuttingcontact with the outer surfaces of the gripping portion of the electriccomponents will cause an increase in a load acting on each chucking jaw108, 109, and an increase in a load acting on each movable element 84,86. The loads acting on the movable elements 84, 86 are monitored by theabove-indicated current detecting portion or load detecting portion, onthe basis of the detected amounts of electric current I applied thereto.The movements of the chucking jaws 108, 109 toward the provisionaltarget positions are terminated when the amounts of electric current Ihave increased to or exceeded a preset threshold value. To this end,step S17 is implemented to determine whether the detected amounts ofelectric current I have reached or exceeded the threshold value. If anaffirmative decision (YES) is obtained in step S17, the generation ofthe movements commands is terminated to stop the chucking jaws 108, 109,so that the electric component can be held or gripped by the chuckingjaws 108, 109 with a suitably controlled holding force.

Then, the control flow goes to step S18 in which the present positionsof the chucking jaws 108, 109 are determined as final target positions.Step S18 is followed by step S19 in which the command to move thechucking jaws 108, 109 at the relatively low speed is replaced by thecommand to move them at the relatively high speed, so that the chuckingjaws 108, 109 are moved at the relatively high speed when step S13 issubsequently implemented for the next electric component. Further, theDECELERATION flag F1 is reset to “0”, in step S19. Then, the controlflow goes to step S20 in which the linear motor 80 is commanded tomaintain the chucking jaws 108, 109 at the final target positions. Itwill be understood that a portion of the control device 116 assigned toimplement steps S18 and S20 constitutes a final-target-position holdingcontrol portion operable to maintain the chucking jaws 108, 109 at thefinal target positions. While the chucking jaws 108, 109 are held at thefinal target positions, the detection of the loads acting on the movableelements 84, 86 is not effected. In this respect, the above-indicatedportion of the control device 116 also functions as a load-detectioninhibiting portion operable to inhibit the detection of the loads whilethe chucking jaws 108, 109 are held at the final target positions. Witha series of steps S11–S20 being implemented, the electric component isheld by the chucking jaws 108, 109 of the chuck 72 with an optimumamount of holding force. In this state, the chuck 72 is elevated in stepS21. In summary, the control device 116 functions as a drive controlportion operable to control the movable elements 84, 86 for controllingthe movements of the chucking jaws 108, 109. The drive control portionincludes the above-indicated drive-commanding portion, movementdetecting portion, provisional positioning control portion, initialpositioning portion, deceleration control portion, final-target-positionholding portion, and load detecting portion, etc.

In FIG. 3, the electric component 134 having the smallest widthdimension that can be held by the chuck 72 is shown by two-dot chainline. The chucking jaws 108, 109 can be spaced apart from each other bya maximum distance which is several times the smallest width dimensionof the electric component. That is, the chuck 72 can hold the electriccomponent whose width dimension is several times the smallest widthdimension. The horizontal dimension of the electric component 134indicated by two-dot chain line in FIG. 2 is the maximum dimension inthe Y-axis direction perpendicular to the X-axis direction in which thechucking jaws 108, 109 are moved when the electric component is held bythe chuck 72. Further, the chuck 72 can hold the electric componentwhose dimension in the Z-axis direction is considerably large, since themaximum distance of movements of the vertically movable member 50 andthe chuck 72 is sufficiently large.

As described above, the movable elements 84, 86 are controlledindependently of each other to control the movements of the two chuckingjaws 108, 109 independently of each other. Although the componentchucking routine of FIG. 10 has been described in the case of thechucking jaws 108, 109 of the type shown in FIG. 7A arranged to hold theelectric component at its outer surfaces, the movements of the chuckingjaws 108, 109 of the type shown in FIG. 7B arranged to hold the electriccomponent at its inner surfaces are controlled in substantially the samemanner as described above, except for the directions of the movements tothe initial positions and the provisional target positions.

After the chuck 72 has received the electric component 134 from thecomponent-supplying device 16, in step S3 of the routine of FIG. 9, thecontrol flow goes to step S4 in which the chuck 72 is moved to apredetermined image-taking position. Step S4 is followed by step S5 inwhich an image of the electric component 134 is taken by the imagetaking device 48 which is provided with the line sensor 46. Describedmore specifically, a movement of the chuck 72 at a predeterminedconstant speed by a predetermined distance in the Y-axis direction isinitiated, to permit the line sensor 64 to take multiple lines of imageswhich collectively define a two-dimensional image of the electriccomponent 134. However, the image taking device 48 provided with theline sensor 46 may be replaced by an image taking device using a matrixof CCDs capable of taking a two-dimensional image of an object at onetime. Image data obtained by the image taking device 48 are comparedwith reference image data indicative of an image of the electriccomponent which has nominal center positions in the XY coordinate systemand a nominal angular position about a vertical axis which passes thecenter of the electric component. This comparison of the image data iseffected by the image data processing computer 130, to obtainhold-position error data of the electric component, that is, tocalculate center position errors ΔX and ΔY and an angular positioningerror Δθ of the electric component 234. The calculated center positionerrors ΔX and ΔY and angular positioning error Δθ are fed from thecomputer 130 to the computer 118 of the control device 116.

Step S5 is followed by step S6 in which the chuck 72 is moved to thepredetermined component-mounting position obtained in step S1, while atthe same time the hold position error data of the electric componentobtained in step S5 are supplied from the image data processing computer130 to the computer 118. The chuck 72 is rotated to eliminate theangular positioning error Δθ of the electric component, and movementdata to move the chuck 72 in the X-axis and Y-axis directions to thecomponent-mounting position are adjusted to eliminate the centerposition errors ΔX and ΔY of the electric component. Then, the controlflow goes to step S7 in which the electric component is mounted at thecomponent-mounting spot on the printed-wiring board 14, according to acomponent mounting routine illustrated in the flow chart of FIG. 11.Namely, the component mounting routine is initiated with step S31 inwhich the chuck 72 is lowered to force the electric component 134 ontothe component-mounting surface of the printed-wiring board 14, so thatthe electric component 134 is temporarily fixed to thecomponent-mounting surface with an adhesive agent already applied to thecomponent-mounting spot. Step S31 is followed by step S32 in which thechuck 72 is opened to release the electric component 134. Then, thecontrol flow goes to step S33 in which the chuck 72 is elevated awayfrom the printed-wiring board 14.

When the electric component has been mounted at the predeterminedcomponent-mounting spot on the printed-wiring board 14, the control flowgoes to step S8 to determine whether the intended component mountingoperation to mount all of the electric components on the board 14 iscompleted. If a negative decision (NO) is obtained in step S8, thecontrol flow goes back to step S1 to repeatedly execute theprinted-wiring-board assembling routine of FIG. 9. If an affirmativedecision (YES) is obtained, the execution of the routine of FIG. 9 forthe present board 14 is terminated.

There will be described a component chucking routine which is executedby the control device 116 according to a second embodiment of thisinvention in place of the component chucking routine of FIG. 10. Unlikethe first embodiment of FIG. 10 wherein the movements of the chuckingjaws 108, 109 are controlled by positioning commands, the present secondembodiment is arranged to control the movements by speed controlcommands. The component chucking routine of FIG. 12 is initiated withstep S41 to move the chucking jaws 108, 109 to the provisional targetpositions at which the jaws 108, 109 are spaced apart from the outersurfaces of the electric component by the same distance, as describedabove with respect to step S11. After the chuck 72 is lowered in stepS42, the control flow goes to step S43 in which movements of thechucking jaws 108, 109 towards each other at a controlled speed areinitiated, so that the two chucking jaws 108, 108 eventually come intoabutting contact with the electric component at the same time. Steps S44and S45 are identical with steps S14 and S15. If an affirmative decision(YES) is obtained in step S45, step S46 is implemented to decelerate thechucking jaws 108, 109, as in step S16, so that the chucking jaws 108,109 come into abutting contact with the electric component at a reducedspeed, with a reduced shock.

Steps S47–S51 are identical with steps S17–S21, except in that step S49is formulated to merely reset the DECELERATION flag F1 to “0”. Like stepS17, step S47 assures an optimum holding force by which the electriccomponent is held by the chucking jaws 108, 109 whose movements havebeen controlled by the speed control commands.

There will next be described a component chucking routine according to athird embodiment of this invention, by reference to the flow chart ofFIG. 13. Unlike the first and second embodiments of FIGS. 10 and 12 inwhich the movements of the chucking jaws 108, 109 are stopped when themonitored or detected amounts of electric current I applied to themovable elements 84, 86 have increased to the predetermined thresholdvalue, the present third embodiment is arranged to move the chuckingjaws 108, 109 toward the provisional target positions according topositioning commands such that the amounts of electric current I to beapplied to the movable elements 84, 86 are limited so as not to exceed apredetermined upper limit. The movable elements 84, 86 are driven withthe limited electric current I, to move the chucking jaws 108, 109 untilall of the positioning commands have been executed. Steps S60 and S61that are identical with steps S11 and S12 are followed by step S62 inwhich drive current limitation of the movable elements 84, 86 isinitiated. Step S62 is followed by step S63 in which the movableelements 84, 86 are driven according to positioning commands to move thechucking jaws 108, 109 to the predetermined provisional targetpositions, as in step S13, but under the drive current limitation of themovable elements 84, 86. Thus, the loads acting on the movable elements4, 86 will not exceed an upper limit corresponding to the upper limit ofthe amounts of electric current I to be applied to the movable elements84, 86, while the movable elements 84, 86 are driven according to thepositioning commands to move the chucking jaws 108, 109 toward theprovisional target positions. Accordingly, the movements of the chuckingjaws 108, 109 toward each other are substantially inhibited after theloads on the movable member 84, 86 have reached the upper limit, so thatthe holding force of the chuck 72 is maintained at the optimum valuecorresponding to the upper limit. Step S63 is followed by step S64 todetermine whether all of the positioning commands have been executed.When an affirmative decision (YES) is obtained in step S64, the controlflow goes to step S65 to maintain the present operating state of thechuck 72 for a predetermined time, for permitting the holding force andposition of the electric component to be stabilized. Then, step S66 isimplemented to determine the present positions of the chucking jaws 108,109 as the final target positions, as in step S18. Step S66 is followedby step S67 to cancel the drive current limitation of the movableelements 84, 86. Then, steps S68 and S69 identical with steps S20 andS21 are implemented. The drive current limitation is cancelled in stepS67, to assure a high response of the movable elements 84, 86 when theyare required to be operated to move the chucking jaws 108, 109 when thechucking jaws 108, 109 are displaced from the final target positions forsome reason or other during the control to maintain the final targetpositions in step S68.

There will be described a component chucking routine according to afourth embodiment of the present invention, by reference to the flowchart of FIG. 14. The component chucking routine of FIG. 14 is similarto that of FIG. 13 in that the movable elements 84, 86 are driven underthe drive current limitation, but is different from the routine of FIG.13 in that the movable elements 84, 86 are driven according to the speedcontrol commands rather than the positioning commands, as in theembodiment of FIG. 12. The routine of FIG. 14 is initiated with stepsS70–S72 identical with steps S60–S62 of FIG. 13. Steps S70–S72 arefollowed by step S73 in which the speed control commands are generatedto move the chucking jaws 108, 109 at a controlled speed. Then, thecontrol flow goes to steps S74–S79 identical with steps S64–S69 of FIG.13. Like the component chucking routine of FIG. 13, the componentchucking routine of FIG. 14 assures an optimum holding force of thechuck 72 owing to the drive current limitation of the movable elements84, 86. It will be understood that a portion of the control device 116assigned to implement steps S67 and S77 of FIGS. 13 and 14 constitutes acurrent limitation canceling portion operable to cancel the limitationof the drive current I to be applied to the movable elements 84, 86.

Referring next to the flow chart of FIG. 15, there will be described acomponent chucking routine according to a fifth embodiment of thisinvention, which is identical with that of the third embodiment of FIG.13, except in that the chuck 72 is elevated before the final targetpositions of the chucking jaws 108, 109 are determined to maintain thechucking jaws 108, 109 at the determined final target positions. In thepreceding embodiments of FIGS. 10–14, the chuck 72 is elevated while thechucking jaws 108, 109 are held at the determined final targetpositions. FIGS. 16A and 16B schematically show a problem which may takeplace if the chuck 72 is elevated while the chucking jaws 108, 109 areheld at the final target positions determined before the elevation ofthe chuck 72. Under some condition, the electric component 134 may beheld by the chucking jaws 108, 109 while the electric component 134 isforced against a surface 135 of the component-supplying device 16, asindicated in FIG. 16A. In this case, a friction force due to a loadacting on a portion “A” of the electric component 134 in the X-axisdirection, or any other external force other than the component holdingforce generated by the chuck 72 acts on the electric component 134. Ifthe chucking jaws 108, 109 are held at the final target positions of thechucking jaws 108, 109 determined under the drive current limitation ofthe movable elements 84, 86, the electric component 134 is freed from aninfluence of the friction force or any other external force after theelevation of the chuck 72 away from the surface 135, so that thecomponent holding force acting on the electric component 134 is reduced,leading to a possibility of falling of the electric component 134 fromthe chuck 72. Under some other conditions, the electric component 134may be held by the chucking jaws 108, 109 with some angle of inclinationof the electric component relative to the chucking jaws 108, 109, whichcauses gaps between the jaws and the outer surfaces of the electriccomponent, as indicated in FIG. 16B. In this case, too, there is apossibility of falling of the electric component 134 from the chuck 72due to reduced component holding force if the chuck 72 is elevated whilethe chucking jaws 108, 109 are held at the final target positions of thechucking jaws 108, 109 determined under the drive current limitation ofthe movable elements 84, 86.

Steps S80–S85 in the component chucking routine of FIG. 15 are identicalwith steps S60–S65 of FIG. 13. Step S85 is followed by step S86 in whichthe chuck 72 is elevated. After the electric component 134 held by thechuck 72 has been moved apart from the surface 135 of thecomponent-supplying device 16, step S87 is implemented to determine thepresent positions of the chucking jaws 108, 109 as the final targetpositions. Step S88 is then implemented to cancel the drive currentlimitation of the movable elements 84, 86. Step S88 is followed by stepS89 in which the chucking jaws 108, 109 are held at the determined finaltarget positions. Thus, the final target positions are determined onlyafter the electric component 134 has been moved apart from the surface135, and the chucking jaws 108, 109 are held at the determined finaltarget positions, which are not influenced by the friction force or anyother external force and which are determined while the electriccomponent is held by the chuck 72 in the nominal posture or attitude.Accordingly, the present embodiment assures an improved degree ofoperating stability of the linear-motor-driven chuck 72.

In the preceding embodiments, the chuck 72 is provided with a pair ofchucking jaws 108, 109 movable toward and away from each other in onedirection by the respective movable elements 80, 86. However, theprinciple of the present invention is applicable to an electricallyoperated chucking apparatus wherein a linear-motor-driven chuck 142 isprovided with a first pair of movable elements 138, 139 movable relativeto each other in a first direction, and a second pair of movableelements 140, 142 movable relative to each other in a second directionperpendicular to the first direction. In this sixth embodiment of theinvention, the linear-motor-driven chuck 142 includes a stator 144 whichhas four arms which correspond to the respective four movable elements138–141 and which extend in respective radial directions such that thefour arms are equiangularly arranged in the rotating direction of therotary shaft 62. Although the configuration and size of the electriccomponents that can be held by the chuck 142 are comparatively limiteddue to a possibility of an interference between the adjacent movableelements 138–141, the electric components of relatively small sizes maybe held by the chuck 142 where chucking jaws are attached to therespective movable elements 138–141 such that the chucking jaws arelocated radially inwardly of the radially inner ends of the movableelements 138–141. This chuck 142 is relatively advantageous in holdingelectrical components of asymmetric configurations.

While the several preferred embodiments of this invention have beendescribed above, for illustrative purpose only, it is to be understoodthat the present invention may be embodied with various changes,modifications and improvements, such as those described in the SUMMARYOF THE INVENTION, which may occur to those skilled in the art. Forinstance, the electrically operated chucking apparatus of the presentinvention is applicable to not only an electric-component mountingsystem, but also any industrial equipment used in various fields of artswherein various components, parts or members are held or chucked for anyspecific purposes.

1. An electrically operated chucking apparatus comprising: anelectrically operated chuck comprising at least two movable membersmovable toward and away from each other, and at least two drive deviceswhich include respective electrically operated actuators operable tomove said at least two movable members, respectively, toward and awayfrom each other; and a control device operable to control said at leasttwo drive devices, and wherein said control device includes: a drivecontrol portion operable to control said at least two drive devices suchthat each of at least one of an actual position and an actual speed ofmovement of each of said at least two movable members changes toward apredetermined target value; and a load detecting portion operable todetect a load acting on said at least two movable members duringoperation of said drive control portion to control said at least twodrive devices, said drive control portion commanding said at least twodrive devices to terminate movements of said at least two movablemembers when said load detected by said load detecting portion hasincreased to a predetermined threshold.
 2. The electrically operatedchucking apparatus according to claim 1, wherein said drive controlportion includes a drive-commanding portion operable to generate controlcommands from time to time, for commanding said at least two drivedevices, so as to control at least one of said actual position and saidactual speed of movement of each of said at least two movable members.3. An electrically operated chucking apparatus according to claim 1,wherein said load detecting portion includes a current detecting portionoperable to detect an amount of electric current applied to saidelectrically operated actuators.
 4. An electrically operated chuckingapparatus according to claim 1, wherein said drive control portionincludes a movement detecting portion operable to detect at least one ofsaid actual position and said actual speed of movement of each of saidat least two movable members, and drive control portion controls said atleast two drive devices on the basis of an output of said movementdetecting portion.
 5. An electrically operated chucking apparatusaccording to claim 1, wherein each of said at least two movable membersis provided with a chucking jaw having a gripping surface engageablewith an outer surface of a gripping portion of an object to be held bysaid electrically operated chuck, and said drive control portionincludes a provisional positioning control portion operable to controlsaid at least two drive devices, so as to move said at least two movablemembers toward each other to respective predetermined provisional targetpositions at which an internal dimension of said electrically operatedchuck generally defined by the gripping surfaces of the chucking jaws issmaller by a predetermined amount than an external dimension of saidgripping portion of said object.
 6. An electrically operated chuckingapparatus according to claim 1, wherein each of said at least twomovable member is provided with a chucking jaw engageable with an outersurface of a gripping portion of an object to be held by saidelectrically operated chuck, and said drive control portion includes aninitial positioning portion operable to control said at least two drivedevices, so as to move said at least two movable members towardrespective predetermined initial positions at which the chucking jaws ofall of said at least two movable members are spaced from the outersurface of said gripping portion of said object, by an equal distance,said drive control portion controlling said at least two drive devicesto move said at least two movable members from said predeterminedinitial positions toward the outer surface of said gripping portion. 7.An electrically operated chucking apparatus according to claim 1,wherein each of said at least two movable members is provided with achucking jaw having a gripping surface engageable with an inner surfaceof a gripping portion of an object to be held by said electricallyoperated chuck, and said drive control portion includes a provisionalpositioning control portion operable to control said at least two drivedevices, so as to move said at least two movable members away from eachother to respective predetermined provisional target positions at whichan external dimension of said electrically operated chuck generallydefined by the gripping surfaces of the chucking jaws is larger by apredetermined amount than an internal dimension of said gripping portionof said object.
 8. An electrically operated chucking apparatus accordingto claim 1, wherein each of said at least two movable member is providedwith a chucking jaw engageable with an inner surface of a grippingportion of an object to be held by said electrically operated chuck, andsaid drive control portion includes an initial positioning portionoperable to control said at least two drive devices, so as to move saidat least two movable members toward respective predetermined initialpositions at which the chucking jaws of all of said at least two movablemembers are spaced from the inner surface of said gripping portion ofsaid object, by an equal distance, said drive control portioncontrolling said at least two drive devices to move said at least twomovable members from said predetermined initial positions toward theinner surface of said gripping portion.
 9. An electrically operatedchucking apparatus according to claim 1, wherein each of said at leasttwo movable members is provided with a chucking jaw engageable with asurface of a gripping portion of an object to be held by saidelectrically operated chuck, and said drive control portion includes adeceleration control portion operable to reduce a speed of movement ofsaid each movable member toward said surface of said gripping portion,when said chucking jaw has reached a predetermineddeceleration-initiating position at which said chucking jaw is spacedfrom said surface of said gripping portion by a predetermined distance.10. An electrically operated chucking apparatus according to claim 1,wherein said drive control portion includes a final-target-positionholding control portion operable to determine, as final target positionsof said at least two movable members, actual positions of said at leasttwo movable members upon detection by said load detecting portion thatsaid load has increased to said predetermined threshold, saidfinal-target-position holding control portion controlling said at leasttwo drive devices to hold said at least two movable members at saidfinal target positions.
 11. An electrically operated chucking apparatusaccording to claim 10, wherein said drive control portion furtherincludes a load-detection inhibiting portion operable to inhibit thedetection of said load while said at least two movable members are heldat said final target positions under the control of saidfinal-target-position holding control portion.
 12. An electricallyoperated chucking apparatus according to claim 10, wherein saidelectrically operated chuck is movable to receive an object to be heldthereby, from an object-supporting member, and saidfinal-target-position holding control portion determine, as said finaltarget positions, the actual positions of said at least two movablemembers after said object held by said electrically operated chuck isseparated from said object-supporting member.